U.S. patent number 3,654,807 [Application Number 05/007,287] was granted by the patent office on 1972-04-11 for angle of attack indicating system.
Invention is credited to Donald Stephen Deskey.
United States Patent |
3,654,807 |
Deskey |
April 11, 1972 |
ANGLE OF ATTACK INDICATING SYSTEM
Abstract
An electronic angle of attack indicating system is provided
which may be used, for example, to indicate the sail trim of a
sailboat, or the angle of attack of an aircraft, or the like, so
that the sail or the aircraft may be maintained at any preset
attack angle. The system of the invention uses a pair of
temperature sensitive devices, such as thermistors, which are
mounted on either side of the leading edge of an airfoil, such as a
sail or wing, and which sense the air flow differential on the
opposite sides of the airfoil, by virtue of the resulting
temperature differences. An electric indicating system coupled to
the temperature sensitive devices indicates the existence of the
air flow differential, so that the appropriate adjustments may be
made to maintain the preset attack angle.
Inventors: |
Deskey; Donald Stephen (Los
Angeles, CA) |
Family
ID: |
21725289 |
Appl.
No.: |
05/007,287 |
Filed: |
January 30, 1970 |
Current U.S.
Class: |
73/180; 116/200;
114/102.1; 73/170.03 |
Current CPC
Class: |
B63B
49/00 (20130101); G01P 5/12 (20130101) |
Current International
Class: |
B63B
49/00 (20060101); G01P 5/10 (20060101); G01P
5/12 (20060101); G01c 021/00 () |
Field of
Search: |
;73/180,188,189,178
;114/102 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Woodiel; Donald O.
Claims
What is claimed is:
1. A system for sensing deviations of a fluid foil from a
predetermined attack angle with respect to the fluid through which
the foil is moving, said system including:
first and second sensors mounted on the foil on opposite sides
thereof and responsive to the fluid stream over the respective
surfaces of said foil for providing electrical indications
thereof;
electrical circuit means connected to said sensors for developing
electrical output signals whenever the fluid flow differential over
the respective surfaces of said foil departs from an optimum
range;
said electrical circuit means including a differential amplifier
connected to said sensors for developing electrical output signals
having an amplitude related to the differential between the
electrical indications provided by said first and second sensors,
and multivibrator networks connected to said differential amplifier
and responding to the output signals from said differential
amplifier to be triggered thereby and indicate the direction and
amount of the aforesaid deviations of said foil from said
predetermined attack angle; and
utilization circuitry coupled to said electrical circuit means for
developing a predetermined control effect in response to said
electrical output from said electrical circuit means.
2. The system defined in claim 1, in which said utilization
circuitry includes indicator lamps connected to said multivibrator
circuits to be selectively controlled thereby.
3. A system for sensing deviations, from a predetermined attack
angle, of the sail of a sailboat which may be sailed on a port or
starboard tack, including:
first and second sensors mounted on the sail on opposite sides
thereof and responsive to the air stream over the respective
surfaces of said sail for providing electrical indications
thereof;
electrical circuit means connected to said sensors for developing
electrical output signals whenever the fluid flow differential over
the respective surfaces of said sail departs from an optimum range;
and
utilization circuitry coupled to said electrical circuit means for
developing a predetermined control effect in response to said
electrical output from said electrical circuit means,
said utilization circuitry including a first section for developing
said predetermined control effect during said port tack and a
second section for developing said predetermined control effect
during said starboard tack, and
further including selection switching means for conditioning said
electrical circuit means and said utilization circuitry selectively
for said port tack and said starboard tack.
4. The system defined in claim 3, in which said utilization
circuitry includes a pair of indicator lights connected to be
selectively energized during the port tack in accordance with a
first parameter, and to be selectively energized during the
starboard tack in accordance with a second parameter.
5. The system defined in claim 4, in which said indicator lights
are located on a single control panel.
6. The system defined in claim 4, in which said utilization
circuitry includes a further pair of indicator lights respectively
connected in shunt with said first-mentioned pair and located on a
second panel.
Description
BACKGROUND OF THE INVENTION
In sailing, it is important that the trim of the sail be maintained
at an optimum attack angle with respect to the wind. By the use of
the system of the present invention, any departure from the optimum
angle of attack is indicated so that appropriate adjustments may be
made.
Effectively, the system to be described provides an indication of
change of angle of attack of the sail from a predetermined setting
in a qualitative manner. As is well known, a sail is similar to the
wing of an aircraft, in that both airfoils develop lift and both
can be stalled. The concept of the invention, therefore, can be
applied to aircraft, or to any airfoil application in which an
optimum angle of attack is to be maintained, although the
particular description to be contained herein will be applied to
the jib of a sailboat.
The sensing elements to be described are temperature sensitive
devices, such as thermistors, which are mounted on either side of
the sail near its leading edge. However, other sensing elements
such as hot wires, or other temperature responsive elements which
may, for example, be mounted on the surface of the sail on either
side near the leading edge, or flush with the wing of an aircraft
on the top and bottom sides near the leading edge, may be used.
Moreover, the sensing elements could take the form of small probes
located in the air stream at the same locations. Alternatively, the
sensing elements may be mounted on a small fixed vane attached to
the leading edge of the sail or wing, or other appropriate devices
may be used.
The sensing elements in the embodiment to be described are heated
by a constant current source and a differential voltage output is
derived. This voltage output is used to energize appropriate
indicator lamps. However, it could be amplified and linearized, and
could then be used to drive an "angle of attack" indicator.
Moreover, if the angle of attack exceeds a predetermined maximum,
which is indicative of a stalling condition, a stall warning horn,
or other indicator could be actuated.
An advantage of the system of the present invention over prior art
systems is that it uses no moving parts. In addition, the sensing
elements may be flush with the sail or wing, as mentioned above, so
as to provide no interference with the proper operation of the
airfoil.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a representation of a sailboat, and showing the manner in
which sensing elements incorporated into the system of the
invention are mounted on opposite sides of the jib adjacent its
leading edge;
FIG. 2 is a block diagram of an electronic system which may be
connected to the sensing elements of FIG. 1;
FIG. 3 shows port and starboard control panels which may replace
the single panel of FIG. 2;
FIG. 4 is a diagram of an appropriate circuit for the system of
FIG. 2;
FIG. 5 is an additional circuit diagram showing the manner in which
the circuit of FIG. 4 may be adapted for use in conjunction with
the control panels of FIG. 3;
FIG. 6 is a top plan view of an appropriate housing for the sensing
elements; and
FIG. 7 is a section, taken along the line 7--7 of FIG. 6.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
As shown in FIG. 1, a pair of thermistors, for example, designated
T1 and T2, which are preferably matched and mounted in housings
which direct the air flow horizontally past the thermistors. The
housing are affixed to the opposite sides of a fore sail, such as
the jib 10, of a sailboat, adjacent the luff or leading edge of the
sail. When the thermistors are matched, there is no need to
readjust the circuit with each change in ambient temperature and
wind velocity. The sailor sets his sail to a certain trim which
hopefully is the optimum trim and which establishes a certain
differential in air flow velocity between the fore face and aft
face of the sail, and the system of the invention measures the air
flow differential to provide an indication of any departure of the
sail from the pre-set trim. At optimum trim, for example, and under
venturi principles, the velocity of air across the fore face is
greater than across the aft face to produce the decreased pressure
on the fore face for the desired airfoil draw effect. As will be
described, the system of the invention is balanced, for example, to
the differential air velocity at which the sail is set, and it
indicates any departure therefrom, since such departure is
accompanied by a change in the differential temperature of the two
thermistors.
The thermistors T1 and T2, preferably matched, are connected to the
electronic circuitry in the system of the invention by means of
leads W1 and W2. A pair of transistors Q5 and Q6 in the electronic
circuitry may also preferably be matched.
As shown in FIG. 2, the thermistors T1 and T2 are energized by
identical current sources 12 and 14. The thermistors are connected
into an input circuit 16 which, in turn, is connected to a
differential amplifier circuit 18. The output from the differential
amplifier circuit is passed through a light control or light driver
circuit 20 which, in turn, is connected to a pair of electric
indicator lights L.sub.1 and L.sub.2 on a control panel 22. The
control panel 22 also includes a light dimmer control P3 which
adjusts the intensity of the lights L.sub.1 and L.sub.2 for
daylight and night time conditions. A port trim control P1.sub.p is
provided on the control panel, as well as a starboard trim control
P1.sub.s. In addition, a trim control selector switch S.sub.2 is
provided so that either of the two trim controls may be
selected.
In the operation of the system, the thermistors T1 and T2 sense any
departure of the angle of attack of the jib from the pre-set angle,
and this is accompanied by the flashing of L.sub.1 or L.sub.2
depending on the direction of the angle of attack deviation from
the pre-set angle. The helmsman turns selector switch S.sub.2
toward trim control P1.sub.p or P1.sub.s to activate the one most
convenient to his steering position on that tack. The helmsman
would then select the other trim control for the opposite tack.
Once the helmsman has trimmed his jib or steered the boat so that
the sail is working at its most efficient angle of attack he then
turns the trim control that he has selected for use on that tack
until neither indicator lamp is flashing. Any change in the angle
of attack from the pre-set angle is then indicated by the flashing
of the appropriate lamp. On a starboard tack, for example, the
flashing of L.sub.1 would indicate a condition of low trim (higher
angle of attack) or near stall, and a flashing of L.sub.2 would
indicate a condition of impending luff (lower angle of attack).
The control panel 22 in FIG. 2 is intended for use in smaller
sailboats, or the like, in which the helmsman has a single compass
and can conveniently see and reach the control panel from his
normal steering positions. However, the larger sailboats in which
the helmsman has two compass positions, two panels 22a and 22b as
shown in FIG. 3 may be provided. One of these panels is located,
for example, on the port side of the craft, and the other on the
starboard side.
The panel 22a, for example, includes the trim control P1.sub.p,
whereas the panel 22b includes the trim control P1.sub.s. The trim
control selector switch S.sub.2 may be located on the port side
control panel 22a. Each panel includes its indicator lights, the
lights L1.sub.p and L2.sub.p being located on the panel 22a, and
the lights L1.sub.s and L2.sub.s being located on the panel 22b.
The dimmer P3 may be used to set the illumination level of the
lights on the port control panel 22a, and a further dimmer P4 may
be provided for controlling the illumination level of the lights
L1.sub.s and L2.sub.s on the starboard control panel 22b.
As shown by the circuit diagram of FIG. 4, the thermistors T1 and
T2 are included in a bridge circuit with a pair of PNP transistors
Q5 and Q6, each of which may be of the type designated 2N3703, the
thermistors being included in the respective collector circuits of
the transistors. The emitters of the transistors are connected
through respective resistors R1 and R2, each having a value, for
example, of 42.2 ohms, to the positive terminal of the
unidirectional potential source of the system, the negative
terminal being connected to the thermistors, as shown.
A pair of diodes D1 and D2 are connected between the positive
terminal and the base electrodes of the transistors Q5 and Q6.
These diodes may be of the type designated IN4001. The base
electrodes are also connected to the negative terminal through a
3.9 kilo-ohm resistor R6. The collectors of the transistors Q5 and
Q6 are connected respectively to the base electrodes of a pair of
NPN transistors Q1 and Q2. The latter transistors may be of the
type designated 2N3711, and are connected as a differential
amplifier.
The circuit described above provides a pair of matched current
sources 12 and 14 for the thermistors T1 and T2, and it causes
current to flow through the thermistors so as to heat the two
thermistors to an appreciable temperature level. As described
above, the thermistors are mounted on opposite sides of the jib 10.
Any change in ambient temperature affects both the transistors to
an equal extent, and does not have any effect on the signal level
between the collectors of the transistors Q5 and Q6, as applied to
the transistors Q1 and Q2. However, any change in the amount of air
flow over one of the transistors with respect to the other,
provides a change in the signal applied to the transistors Q1 and
Q2, the sign and magnitude of which depends upon the sense and
magnitude of the change in the air flow. This change in air flow
can be related to the sail trim, as described above,
As mentioned above, the transistors Q1 and Q2 are connected as a
differential amplifier. The collectors of the transistors are
connected through respective 6.2 kilo-ohm resistors R4 and R5 to
the positive terminal of the unidirectional potential source, these
resistors being shunted by respective 2 microfarad capacitors C5
and C6. The emitters of the transistors are connected to the trim
control selector switch S.sub.2, as shown, as are a pair of trim
control potentiometers designated P1.sub.p and P1.sub.s, which are
controlled by trim control knobs designated P1.sub.p and P1.sub.s
on the control panel 22. The switch S.sub.2 is a double-pole
double-throw switch connected as shown. The potentiometers P1.sub.p
and P1.sub.s may each have a value of 25 kilo-ohms.
A 3.3 kilo-ohm resistor R.sub.3 and Zener diode D3 are connected
across the unidirectional potential source, the junction of which
is connected to a resistor R7 which may, for example, have a
resistance of 39 kilo-ohms. R.sub.3 and D3 provide a stabilized
reference voltage for the constant current source formed by R7, P2,
R13, T3, Q7 and Q8. The resistor R7 is connected to a 7.5 kilo-ohm
potentiometer P2 which, in turn, is connected to the base
electrodes of a pair of NPN transistors Q7 and Q8, which may be of
the type designated 2N3711. P2 is a sensitivity adjustment to vary
the amount of deviation from optimum before the lights flash (dead
band). The collector of the transistor Q7 is connected to its base,
and the collector of the transistor Q8 is connected to the trim
control selector switch S.sub.2. The emitter of the transistor Q8
is connected to the negative terminal of the unidirectional
potential source, and the emitter of the transistor Q7 is connected
to that terminal through a 100 ohm resistor R18. The resistor R18
is shunted by a temperature compensating thermistor T3. The
potentiometer P2 is mechanically coupled to a switch S1 in the
positive lead from the unidirectional potential source, so as to
turn the switch S1 off when the potentiometer P2 is turned to its
maximum resistance value.
The transistors Q1 and Q2 of the differential amplifier are emitter
coupled, the emitter being connected through either the
potentiometer P1.sub.p or P1.sub.s (depending on the setting of the
switch S.sub.2) to an adjustable current source provided by the
circuitry of the transistors Q7 and Q8. This circuit in the common
emitter leg of the differential amplifier serves to improve the
common mode rejection characteristics of the circuit, and also
improves the power supply voltage rejection ratio. Specifically,
this circuit (and particularly the elements R18 and T3) serves to
render the differential amplifier essentially immune to any effect
that changes in ambient temperature might have on the bridge
network in the input circuit 16, or from any effect that changes in
battery voltage might have on the bridge network.
The collector of the transistor Q1 of the differential amplifier is
connected to the base of a PNP transistor Q3, whereas the collector
of the transistor Q2 is connected to the base of a PNP transistor
Q4. Each of these latter transistors may be of the type designated
2N3703, and they are connected as emitter followers. The collectors
of the transistors Q3 and Q4 are connected through respective
resistors R16 and R17 to the negative terminal, each of these
resistors having a resistance, for example, of 91 kilo-ohms.
The collector of the transistor Q3 is connected through a current
limiting resistor R30 to the base of an NPN transistor Q11, whereas
the collector of the transistor Q4 is connected through a current
limiting resistor R31 to the base of an NPN transistor Q14. The
transistor Q11 and an NPN transistor Q12 form a "port"
multivibrator; and the transistor Q14 and a further NPN transistor
Q13 form a "starboard" multivibrator. The transistors Q11, Q12,
Q13, Q14 may each be of the 2N3711 type. The collector of the
transistor Q11 is connected to a 1 microfarad coupling capacitor C1
and through an 8.2 kilo-ohm resistor R8 to the positive terminal;
and the collector of the transistor Q14 is connected to a like
capacitor C2 and to the positive terminal through a like resistor
R13.
The capacitor C1 is connected to the base of the NPN transistor Q12
and through a 91 kilo-ohm resistor R9 to the positive terminal. The
capacitor C2 is connected to the base of the NPN transistor Q13 and
to the positive terminal through a like resistor R12. The collector
of the transistor Q12 is coupled back to the base of the transistor
Q11 through a trimming capacitor C3 of 10 microfarads, and a
similar capacitor C4 is connected to the collector of the
transistor Q13 and base of the transistor Q14. The collector of the
transistor Q12 is connected to the positive terminal through a 3.9
kilo-ohm resistor R10, and to the resistor R20; whereas the
collector of the transistor Q13 is connected to the positive
terminal through a 3.9 kilo-ohm resistor R11 and to the resistor
R22. A 22 micro-microfarad RF protective capacitor C20 is connected
across the source of unidirectional potential. The multivibrators
are connected to respective switching transistors Q9 and Q10.
Resistors R20 and R22 are included in the base circuits of the
latter transistors. The switching transistors Q9 and Q10 may be of
the NPN type designated 2N5449.
The circuitry described above of the light control or light driver
section 20 serves to buffer the two outputs of the differential
amplifier so as to increase the output impedance of the amplifier.
In this way a current source is provided for the multivibrators,
allowing for use of smaller trimming capacitors C3 and C4.
The potentiometer P2 serves to adjust the current source for the
differential amplifier, thereby adjusting the dead band as
mentioned above. The potentiometer P2 is such that over a small
band centered about the point of perfect sail trim, the output from
the differential amplifier is essentially zero. Under these
conditions, the voltage output is insufficient to trigger the
multivibrators in the light driver section. A small, adjustable
dead band is provided, therefore, so that the sail trim can depart
to a certain extent on either side of the perfect setting without
triggering the light driver circuitry multivibrators.
The two controls represented by the potentiometers P1.sub.p and
P1.sub.s are selectively connected into the circuit by the selector
switch S.sub.2. The purpose of having two controls, rather than
one, to pre-select the setting, is so that the setting need not be
changed for each change in tack.
The potentiometer P1.sub.p sets the output from the differential
amplifier to zero for the desired sail trim during, for example,
the port tack, and the potentiometer P1.sub.s sets the differential
amplifier output to zero for the desired sail trim during the
starboard tack. The switch S2 permits the helmsman to place, for
example, the potentiometer P1.sub.p into the circuit during the
port tack, and to place, for example, the potentiometer P1.sub.s
into the circuit during the starboard tack.
During the port tack, for example, and when the potentiometer
P1.sub.p is connected into the circuit by the switch S2, the
potentiometer P1.sub.p may be set so that the output from the
differential amplifier is insufficient to trigger either
multivibrator formed by the transistors Q11/Q12, or Q13/Q14, when
the sail is maintained at the optimum attack angle. Each
multivibrator then remains in its quiescent state, during which the
indicator lamps L.sub.1 and L.sub.2 are off. It will be noted that
each of the multivibrators Q11/Q12 and Q13/Q14 has a relatively
fixed light-on period, and an adjustable or variable light-off
period.
Now, should the sail depart from its optimum attack angle in one
direction, and exceed the normal dead band or range referred to
above, a sufficient signal is produced from the differential
amplifier to trigger the multivibrator formed by the transistors
Q11, Q12 and cause the transistor Q9 to be pulsed, so that the
indicator lamp L.sub.1 flashes. Since the cross-coupling between
the two halves of the multivibrator Q11, Q12, through the
respective capacitors C1 and C3 has no DC path, the multivibrator
returns to its quiescent original state, to be retriggered again
and again so long as the output signal of the differential
amplifier is sufficient. It returns to its quiescent state only
when an attack angle within the dead band has been reestablished.
Should the sail depart from its optimum attack angle in the other
direction, the differential amplifier triggers the multivibrator
formed by the transistors Q13 and Q14 to cause the lamp L.sub.2 to
flash. The lamps flash at a rate which increases as the sail
departure from the preset angle increases. During the starboard
tack, for example, the potentiometer P1.sub.s is connected into the
circuit by the selector switch S.sub.2, and it is preset to cause
the same control to be exerted on the indicator lamps whenever the
sail departs from the preset angle for the starboard tack.
Experienced sailors for many years have been using yarn or tape
telltales on both sides of their headsail luff to give an
indication of sail trim. When sailing in good trim, both telltales
stream back parallel to the sail, following the smooth flow of air
over both sides of the sail. When the jib is trimmed too tight or
one is sailing too low, the leeward telltale flutters indicating
that the sail is stalling. Conversely, if one is too high, the
weather telltale flutters indicating that the sail is approaching a
luff. The system of the invention is designed to display this
information about airflow across the sail in a similar manner. The
red light L.sub.1 represents the telltale on the port side of the
sail and the green light L.sub.2 the starboard. When the instrument
is properly set, the red light will flash under conditions that
would cause the port telltale to flutter, and the green light will
flash to represent a fluttering of the starboard telltale. When
neither light flashes the sail is in trim and the airflow is smooth
and efficient.
For the system of FIG. 3, the same circuit such as shown in FIG. 4
may be used. The only change would be to connect the indicator
lights L1.sub.p and L2.sub.p of the port control panel of FIG. 3
into the circuit, as shown in FIG. 5, in place of the indicator
lamps L.sub.1 and L.sub.2, and to provide blocking diodes D4 and D5
which may be of the type designated IN4001. The indicator lights
L1.sub.s and L2.sub.s of the starboard control panel are connected
in parallel with the original circuit through the starboard dimmer
potentiometer P4, as shown in FIG. 5. Two further blocking diodes
D6 and D7, which also may be of the type designated IN4001, are
included in circuit with the latter control lamps. In the latter
circuit, the controls derived from the system energize both the
lamps L1.sub.p and L1.sub.s, or both the lamps L2.sub.p and
L2.sub.s simultaneously, and at illumination levels as established
by the respective dimmers P3 and P4.
The system above has been described as being powered by direct
current. As will be obvious to those skilled in the art, the system
may also be operated as a carrier system, with AC excitation on the
bridge, the output being fed to an AC amplifier, synchronous
demodulator, and then into the multivibrator.
An improved indicator system is provided, therefore, by which the
trim of the sails of a sailboat may be controlled to maintain the
optimum attack angle. As mentioned above, the indicator system may
also be used in conjunction with the wings of aircraft, or the
like, and in any environment in which a predetermined attack angle
is to be maintained.
The thermistors T.sub.1 and T.sub.2 may be mounted in respective
housings, such as the housing 100 in FIGS. 6 and 7. The housing 100
is formed, for example, of appropriate plastic material. The
housing includes mounting holes 102 which permits it to be mounted
on the sail 10 of FIG. 1. The housing defines a passageway 104
which extends from one end of the housing to the other and through
which the airstream to be sensed passes. The leads of the
thermistor T.sub.1 are protected and supported by suitable
dielectric encapsulation, and potted into a transverse slot 110.
The thermistor T.sub.1 itself is thus held in the air stream
flowing through the passageway 104.
The housings for the respective thermistors T.sub.1 and T.sub.2 are
mounted back to back with the sail 10 sandwiched between. To
protect the thermistors prior to mounting on the sail 10, a thin
wall 112 covers the open side of the passageway 104.
The serpentine character of passageway 104 protects the thermistor
T.sub.1 from damage and from the elements, while still limiting the
flow sensing to horizontal air flow contiguous to the sail 10.
While the system has been designed particularly for airfoils and
more specifically the sail of a sailing vessel, it will be readily
apparent that the structure and concepts here disclosed are also
applicable to any fluid foil, be it airfoil or hydrofoil.
* * * * *